1. Field of the Invention
The invention relates to a friction lining which a device for transmits torque, in particular friction clutches, synchronizers or brakes, the friction lining being fastened on a carrier body in order to form a friction surface and the torque being transferred to a counter surface, whereby the friction lining is constructed from at least two different, porous layers, of which one is fastened on the carrier body. The porous substrate, made of a cellulose base with synthetic fibers and filler, exists as a support for the friction layer, which is also porous, fastened to the substrate and is made of fibers bonded with a thermoset resin.
2. The Prior Art
It is well-known to provide devices for transferring torque by means of friction between surfaces that are pressed against each other, such that at least one of these friction surfaces has a friction lining in order to increase the friction force between the two surfaces. In this regard, there are dry running and wet running friction pairings. The dry running friction pairings can be produced with relatively little complexity, but they are subject to a relatively high wear, so that they are used only when few demands are posed on the transfer of torque or the friction surfaces slide on each other for only a short period of time. In contrast, the wet running friction pairings are cooled with a fluid or lubricant, so that they exhibit higher resilience.
Such a wet running friction lining is known from DE-OS 27 44 944, which describes a synchronizing ring for synchronizing a gear in gear couplings, whose friction lining consists of friction material formed on an organic foundation, thus a so-called paper lining, which is bound together as the friction surface.
The paper lining is made of a material such as cellulose fibers, asbestos fibers, mineral and metal fibers and fillers, and is saturated with a synthetic resin.
Furthermore, it is known, especially for synchronizing devices for motor vehicle manual transmissions, to use sintered friction linings as well as friction linings made of different metals or metal alloys, in particular titanate-based and molybdenum-based friction linings, which are usually sprayed on the carrier surface of a synchronizer ring made of metal. However, friction linings of this kind are relatively expensive to manufacture and do not always exhibit satisfactory frictional properties.
EP 0 162 393 B1 describes a synchronizing ring whose carrier surface is provided with a separately pre-finished friction body, which is constructed from a carrier plate with a powder metal friction lining which is scattered on the carrier plate, subsequently sintered and then compacted. This separately manufactured friction body is finally affixed on the carrier surface of the synchronizer, e.g., by welding. When a suitable powder mixture is used to manufacture the sintered lining, this friction lining exhibits a high stability and also good frictional properties. However, the number of steps required for the production is relatively high because the separately finished synchronizer has to be first manufactured, subsequently finished and then bound to the friction surface.
Finally, another friction pairing for clutches or brakes is known from DE-OS 36 09 879, of whose friction surfaces at least one is composed of a friction lining produced by sintering. However, the friction lining is sintered directly on the friction surface of the carrier body, so that a separate production of the friction body and affixing on the carrier surface by means of its own carrier plate are dispensed with. As in the production of the flat friction discs, the scatter-sinter friction lining is fastened on an annular, flat carrier body, which then as a complete ring with one or more sintered friction surfaces is transformed into a cylinder or cone by deep drawing and finally calibrated and compacted. Thus, the manufacture of a friction ring with a scatter-sintered friction lining is significantly simplified. However, the advantages of a friction lining produced by sintering, especially the high stability to high loads, remain totally unaffected.
On the whole, the prior art wet running friction linings are made of a homogeneous friction material, which are affixed, e.g., bonded, welded, sprayed or sintered, directly on the carrier element. The result is automatically that the active components of the friction material have to be distributed homogeneously through the entire friction lining, in particular its entire thickness, in order to ensure that the components that develop the friction are present on the upper surface of the friction lining that transfers the torque to the counter-surface. However, in the case of a highly effective friction lining with high stability, the active components are expensive, e.g., carbon/carbon compound material or aramide fibers. Since a relatively large amount of this expensive friction material is necessary to manufacture such a friction lining, the lining is also relatively expensive. Friction linings produced on the basis of paper or cork are less expensive, but exhibit also lower performance. Friction linings made of sintered metal are also less expensive.